Magnetic volume control



u y 1950 J. L. RENNICK I 2,515,255

MAGNETIC VOLUME CONTROL Filed June 7, 1949 I F/gl At tenuotion (d b) 8 3O 6O 90 Degrees Rotation JOHN L. RENNICK INVENTOR.

HIS AGENT Patented July 25, 1950 2,51 ,255 MAGNETI Q WE. N'l QL John L. Rennick, Eimwccd Park, 11L, assi nor to Zenith Ejatiio Corporation, a corporation civil-1i This invention relates to magnetic volume control. arrangements which may Ice-used, forv example, in radio transmitting or receivin apparatus.

Customary: volume controlE arrangements used;

inconventional radio apparatus comprise apodesired signal. Fu therm ore sliding contact a1;

rangements are. subjecttq defective operation as a result of the accumulation of dirt, dust, or other extraneous matter.

In' order. to rovidea volume-control. without theiuse. of sliding vcontacts, therehymo overcome these defects, it has been proposed to empio a ic eld w ichis cqnt olla le astqpgeenitilde and/or direct'on to control thearnou oi tr nt flow ng ta tle muta t 9:

electron space c l 7 node of n mnlifi tubet A ran em n s of th s typewhich'hav ,heen proposed heretqfgre are chanwte'rized bya 1' itedcoptrol ran e; th t e. vo a hecoutpu Q Qlli the on: rolled thr e e ta su fie nt iw e amp ude range o satisfyth neql ilr me ts .qtsoim ppli: c t on t i a mp rtant qhiectmpf th m sentinrear 1. 1 ei' saxie er v Pie. as. w mas as q 9 11. con o ansem at'wh h a qxq s w er we: t lt ilt ob ai l b t euse 9 mev slv Sug est d de ange en of h tim ti also dssi s tpett eu erl in euq ib a plifi erslof radio receivers, to providea certain amount of low frequency emphasis orloass boo's't', since the responseicharacteristics of audio any plifiers may otherwise tend to fall on atiotv freduencies. 'Qne well-known methodli o r opta'ining the desired bass boost is toj employ a low 'freguen-cy emphasis circuit tapped from a conventional volunie control potentiometer. Arrangernents of this type, however rnay' not provide sufficient low frequency emphasis at Iow townie levels.

Accordingimit is a further object ofthe present invention to' provide a magnetic volume control arrangementtvhichaaffords in addition to an increased control range over that of a conventional magnetic volumetcontrol, alow frequency em phasis or bass boost which increases continuously with decreasing volume level.

s In accordance with the invention, a r magnetic volume control comprises an electron discharge device having a cathode, an-input e1ect1tode ,vanda pair of anodes. Aninput circuitis jcoupledttothe input. electrode. and tc-tthe. cathode, and ailzputput circuit is coupled tonne of the, anodes and tupthe cathode. In order toncontrol:thetvQLtagein-tthfi output circuit over a. predetermined cQntr-Ql ran thereis provided means externaLto-tthe; deyiceyioi producing, within the. de'viceasvariablema l qtic field fordetermining. the. electron space cunrent distribution between the. anodes.- ;,Aloadgcircuis coupled to th Other anodeeandqto-athecathe e, and a degenerative feedback circuit i coup1ed from the load:circuittoetheinput circuitttofm crease the control range.

The features, as henlesent-inten iqn which areiheiieved to the novel-tare; set ionth withimnticularity in the appended claims. ThQ,iI}QI;1: ti-on, together with further.:obiectsandedvantages thereof, may best e. unde stcod, .howeven h efe nc to the follqwinga-d s ip ionata cnain conne t n wit -r. the amp naming draw ng-in the several fi ure 0i which-l ke 1 xefenence; n11: m ra s ndicat l kee ements.. v and intwl-hichz F ure 1 is, a s hematic; fiilifitli ailia -l-fflmwb r a ma netic vo ume contm qns ructedintaccord: anc t .:t e present inysn ien;

Figure. 2 is a gra cal rep ese tation 9 t; :1 on- 12 7.0 :c arac eristic 1 i the v lume controlperms.- ure 1;

Figure 3t-isa schematic circuit diagmmtQf-Van: other embodiment-inf the-invention;-

Figure 4 a side ,view partly .in; section, of; a portion of aphysica em ime t-of thetinvem tion, and 1 Figure 5 is, arsectional view takensalon ithetiine ;:5 of F gures The magnetic volume. contitolcorfiigure 1.0mm prises an electron: dischar e: dev1ce.=;l l1 havin a cathode ih -input lectrode; 1' 2 and a pa 91 anodes-l3 nd 14. In-"the illustrated emhodim nt, electron discharge device In .Of attypeesinnlarg. to t at desi n ted: GAQ5; anode '13" is Cathode II is conne .An: inpu ir s un d. tq in ut. ec todeait dtc athode H h aus 7 a, pair oiinp t Enamels nne edtio lex in t t1; n. t e sec nd detect r. e a sn e he ,r. receiver no :shcwnt I put coupledlto inpu Qkc lFpdfif zath Q calm condenser intend. n utieleet ede L stens}?! vve to ground through a grid resistor 2|. Input terminal i9 is directly connected to ground. First anode or screen grid 13 is connected to a suitable source of positive unidirectional operating potential, conventionally designated B+, through a load circuit comprising a resistor 22. The other anode i4 is connected to the source B-1- through an output'resistor 24.

In accordance with the present invention, a permanent magnet 25 is rotatably mounted around the envelope of electron discharge device 10, so that rotation of magnet 25 varies the intensity of the magnetic field component transverse to the electron stream within device l0. A degenerative feedback circuit, comprising a blocking condenser 26 and a coupling resistor 21, is coupled from load resistor 22 to input electrode l2 of device 10. Rotation of magnet 25 varies the voltage in output resistor 24 to provide volume control over a predetermined control range, and the degenerative feedback through blocking condenser 26 and coupling resistor 21 operates to increase this control range.

/ In operation, device l and its associated circuits operate as an audio-frequency amplifier. In the absence of magnet 25 and the degenerative feedback circuit, audio-frequency input signals applied between terminals 18 and 19 are amplified in conventional fashion, the amplified voltage outputap'pearing across output resistor 24 due to current flow in the circuitof anode M. This amplified output may be coupled to a second stage of audio-frequency amplification (not shown) or may be utilized in any other desired manner.

- In the position shown, with magnet 25 disposed to direct the entire magnetic field in a direction transverse to the electron stream, it has been found that magnet 25' operates to divert much the greater'portion of the electron space current from output anode M to first anode or screen grid l3; hence, in this condition, the voltage appearing across output resistor 24 is greatly'attenuated due to the decrease of current in the circuit of anode I4. As magnet'25 is rotated,'for example in the direction shown'by the arrow, the intensit of the magnetic field component transverse to the electron' stream within device in is decreased, and as a result, the electron space current distribution between anodes l3 and I4 is varied so that the portion of the space current reaching output anode 14 increases and the portion of the electron space current reaching the other anode 13 decreases. the transverse component of the magnetic field intensity is continuously decreased. Consequent ly, rotation of magnet 25 provides a continuous control of the output voltage overa predetermined control range.

By providing degenerative feedback from load resistor 22 to the input circuit of device I 0, it has be'enfound that the rangethroughout which the output'voltage may be controlled is materially increased. This observed increase in the output voltag'e'control range is attributed to the fact that the voltages appearing in load resistor 22 and in output' resistor 24 are complementary; that is; as the voltage across output resistor 24 increases, the voltage across load resistor 22 decreases due to the variation in the electron space current distribution between output anode I4 and the other anode l3. Thus, when magnet 25 is oriented in the position shown and the output As magnet 25 is rotated through 90,

circuit is degenerative, this feedback operates to reduce the output voltage level still further. Similarly, when magnet 25 has been rotated in the direction shown through an angle of the output voltage is at a maximum level and the voltage across load resistor 22 is at a minimum; thus, in this condition, the degenerative feedback is very small and has little efiect. The net result is that the degenerative feedback circuit from load resistor 22 to the input circuit cooperates with the rotatable magnet structure to provide a material increase in the control range of the output voltage over that obtainable with prior magnetic volume control arrangements.

Figure 2 is a graphical representation of a control characteristic of the arrangement of Figure 1. In Figure 2, decibel attenuation is plotted as a function of the angular position of magnet 25 with respect to the electron stream. Curve 28 represents the control characteristic for a magnetic volume control similar to that shown in Figure l but without degenerative feedback to the input circuit. From curve 28, it is observed that the overall control range from 0 to 90 rotation of the magnet is about 28 decibels. Curve 29 represents the control characteristic obtained when degenerative feedback from the auxiliary anode to the input circuit is employed in combination with the movable magnet. It is observed that this combination affords a. control range of about 43 decibels, representing a material increase over the control range obtainable without degenerative feedback.

For magnet positions from 90 to 180, the control characteristics are substantially symmetrical about the 90 abscissa with respect to curves 28 and 29.

Figure 3 is a schematic representation of another embodiment of the invention utilizing a somewhat different type of electron discharge de vice. The electron discharge device 30 comprises a. cathode H, an input electrode l2, a screen grid BI, and a pair of anodes 32 and 33. Cathode H is directly connected to ground, and screen grid 3! is connected to source B+. Input terminal I8 is coupled to input electrode l2 through a coupling resistor 34. Anodes 32 and 33 are coupled to the positive terminal of a suitable source of positive unidirectional operating potential, here shown as a battery 35 bypassed to ground by means of a condenser 36, through load resistor 22 and output resistor 24 respectively. A pair of output terminals 31 and 38 are provided, terminal 31 being coupled to output anode 33 by means of a coupling condenser 39, and terminal 38 being directly connected to ground.-

Instead of a permanent magnet, the system of Figure 3 utilizes an electromagnet 40 such as a solenoid coaxially disposed about device 30. One terminal of solenoid 40 is directly grounded, and the other is connected to a variable tap 4| on a potentiometer 42 which is connected across battery 35.

voltage across load resistor 22 is'high, and since the feedback from load resistor 22 to the input The degenerative feedback circuit from load resistor 22 to the input circuit comprises blocking condenser 26 and series resistor 21. The time constant of the feedback circuit comprising condenser 26 and resistor 21 is selected to give a desired low frequency emphasis characteristic; for example, a time constant: of .01 second affords effective emphasis for frequencies up to cycles per second. It is contemplated that other types of tone control circuits may be employed in the degenerative feedback circuit for controlling the tan. 1

'; Iii?thefisystembf'FFigmdBfanodes 327E116 33 oi device 130; arefdispb'sef'cl adjacent eai hfoth a common. lane. andifthe magnetic "field' i di= recte'd. vertically with irespe'ctto "the" plane 'oi the drawing. I Y'With'fifthisarran ement, it" isiper'naps easier to understand how thei'ma'gf rieticfieIdVariations' -res1iltj in 'chainges'j;irf,. the" :elebtrpn spa'ce current'idis'tiibution betweenalie anodes. when variable-tap Zllfon'potentiometerf 4? isffrnoyed to the ground term-marine*magnetictfieie worm duce'cl jwithinithe device. 30. .1 Device "30. ;is"construct'ed so that'in'tlii's .cofiditionthe entire ele'c-v tron space current flows to"output ano'def33. W-hentap 4| is, moved to theopposite terminal of. potentiometer 42;.fa .m'axim'um iriagrietic' field is reproduced Withinithe."tub'a'jandthis" fie1d is directedipeir'p endi'cularl'v' Withrespectto" the "plane ofl the-;drawing; and ,traiisyerse' to? 'thfelectr'on stream." The effect "of thisveitticalmagrietic field is etol-de-fie'ct the electrons in atlir'ection perpendicular both to the jelectronistreamfand" to the direction of. .the m'a'gnetic field; the maximum magnetic Ifiel'ci intensity iis-v made; ,siiflici'entl'y great that the {entire electron 'spa cejcurrenti'is' diverted from ioutputanodl 33f to" the auxiliaryfanode 32f. Thus',the..vo1ta'gc appearingfin 'ofutpiut resistor 24 may. be .coiitrolledf'roml a maximumheaten 4 I is at ground potential to auniinimmnwne ta 4 l is connected to th'fhigh "potentialttermirial of potentiometer 32', and the 'volta geiin 'l'ofad1 resistor 22 'var-iesin,a manner complementary 'to'the output voltage variations.

The degenerative feedbaclsf-rom load resistor 22 to the input circuit results in a material increase in "the outputvoltage control range as explained in connection withiigurelb Moreover, the provision of .condense'r- ZSa'nd resistor 21 results additionally in .the provision of a substantial effective bass boost or IIQWJre uency emphasism Furthermore,sinceithellbass boostc'irmiit is connected in'the degenerative" feedback loop from the auxiliary anode to the input circuit, the amount of efiective low frequency emphasis increases continuously with decreasing output volume level. Other types of frequency selective networks may be employed in the feedback circuit to provide any desired frequency and/or amplitude response; with any such arrangement, the amount of tone control action increases continuously with decreasing output volume level.

As an alternative arrangement, instead of varying the axial magnetic field intensity within device 30 by changing the position of tap 4| on potentiometer 42, the desired field intensity variation may be provided by arranging solenoid 40 to be movable axially with respect to device 30 and by exciting solenoid 40 from a constant potential source.

There is shown in Figure 4 a fragmentary view partly in section of a portion of a radio receiver embodying a magnetic volume control such as that described in connection with Figure 1.

Electron discharge device I is mounted on a chassis 45, and suitable circuit connections (not shown) are provided to connect device In in a. circuit similar to that of Figure 1. Permanent magnet 25, which may be of the horseshoe type, is secured to a shaft 45 as by means of a pair of nuts 41 and 48. Shaft 46 bears a control knob t9 and is rotatable in a bushing '50 extending through the wall ofa radio cabinet. In this manner, magnet 25 may be rotated with respect to device It, thereby to vary the intensity of the "Figure- Bis a transverse section taken alongthe lines 5+5 rof Figure '4; menace a re resentatics-or til internal electrodearrangement'br de vice-4 position il- When the"inagnefi 2'5 in the lustrate'd ismztfaliePto 't-he plane" eta-cede W, the magnetic field-intensity com onent-trans erse*to the elctronstreamis at a maximum and thevolumeortheouteut cireaitis atamirii u'mn' Merely by waybf illustration, and in no"-- sense Condenser 25,-0.-l-1m-icrofaradn Resistor 21.,Z..0.-1 me gohm- Magnet 25, a ring type permanentrmagrietirotatably. mounted with respect to device into provide a magnetic field directed transversely of theelectron stream; I

Since 5 the presefitfifiveiition' is dii' ec't'd to tlie combination bra particular:type csuegeserauve feedbacki'rcuit with a m'a'gnetic volume control device; he martian-lav structure bathe-electron fdis'charge' deviceandthe :-=manner in tvliichi the magnetic field is-'applied are-*n'o't to =b the"' illustrated embodimentsan tilized 'so-long' gas variation inth intensity*and/ordirectioir-fofthe m'agn etic' fleld res'ultsl in a continuous change in the: electron space current distribution between two-"anodes. 'Imaccordance with theinverition', onedr the" anodesis utilised-amen butp'ut elem trode; and a degenerative feed-back"bircuitds'con nected between the other anode and the input c i'n enter-thee1anon-dischargedevice;

Thus, the present invention provides an improved magnetic volume control circuit having a control range materially greater than prior magnetic volume control arrangements. As an additional feature, by providing one or more frequency selective networks in the feedback circuit, tone control action which increases continuously in effectiveness with decreasing output voltage level may be provided. The arrangement may find advantageous application in the radio-frequency and intermediate-frequency stages of a radio receiver as Well as in the audio-frequency stages.

While particular embodiments of the present invention have been shown and described, it is apparent that various changes and modifications 50 may be made, and it is therefore contemplated in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. A magnetic volume control system comprising, in combination: an electron discharge device having a cathode, an input electrode, and a pair of anodes; an input circuit coupled to said input electrode and to said cathode; an output circuit coupled to one of said anodes and to said cathode; means external to said device for producing a variable magnetic field within said device for determining the electron space current distribution between said anodes in accordance with said field thereby to control the voltage in said-output circuit over a predetermined control range; a load circuit coupled to the other of said anodes and to said cathode; and a degenerative feedback circuit coupled from said load circuit to said input circuit to increase said control range.

2. A magnetic volume control system comprising, in combination: an electron discharge device having a cathode, an input electrode, and a pair of anodes; an input circuit coupled to said input electrode and to said cathode; an output circuit coupled to one of said anodes and to said cathode; meansexternal to said device for producing a variable magnetic field within said device for determining the electron space current distribution between said anodes in accordance with said field, thereby to control the voltage in said output circuit over a predetermined control range; a load circuit coupled to the other of said anodes and to said cathode; and a degenerative feedback circuit coupled from said load circuit to said input circuit to increase said control range and including a frequency selective network to provide a tone control of increasing effectiveness as said output voltage decreases. 3. A magnetic volume control system comprising, in combination: an electron discharge device having a cathode, an input electrode, and a pair of anodes; an input circuit coupled to said input electrode and to said cathode; an output circuit coupled to one of said anodes and to said cathode; a permanent magnet external to said device for producing a magnetic field within said device and movable relative thereto to vary said field for determining the electron space current distribution between said anodes in accordance with said field, thereby to control the voltage in said output circuit over a predetermined control range; a load circuit coupled to the other of said anodes and to said cathode; and a degenerative feedback circuit coupled from said load circuit to said input circuit to increase said control range.

4. A magnetic volume control system comprisins. in combination: an electron discharge device having a cathode, an input electrode, and a pair of anodes; an input circuit coupled to said input electrode and to said cathode; any output circuit coupled to one of said anodes and to said cathode; electromagnetic means external to said device for producing a variable magnetic field within said device for determining the electron space current distribution between said anodes in accordance with said field, thereby to controlthe voltage in said output circuitover a predetermined control range; a load circuit coupled to the other of said anodes and to said cathode; and a degenerative feedback circuit coupled from said load circuit to said input circuit to increase said control range.

5. A magnetic volume control system comprising-in combination: an electron discharge device having in the order named a cathode, an input grid, a screen grid, and an anode; an input circuit coupled to said input grid and to said cathode; an output circuit coupled to said anode and to said cathode; means external to said device for, producing a variable magnetic field within said. device. for, determining the electron space current distribution between said anode and said screen grid in accordance with said field, thereby to control the voltage in said output circuit over a predetermined control range; a load circuit coupled to said screen grid and to said cathode; and a degenerative feedback circuit coupled from said load circuit to said input circuit to increase said control range.

JOHN L. RENNICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Demuth Dec. 24, 1940 

